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How to Measure SWR on a Coaxial Line

Standing wave ratio (SWR), also known as voltage standing wave ratio (VSWR), is a measure of the ratio between a reflected signal and a direct radio frequency signal as they are received by an antenna. Ham radio operators often test the SWR of their coaxial antenna lines to determine the efficiency of their antennas and how to best place them. You measure the SWR of your coaxial amateur radio antenna line with an SWR meter that is sold specifically for this purpose by ham radio equipment retailers.

Things You'll Need

SWR meter

Instructions

- 1
  Disconnect the antenna coaxial line from your ham radio transceiver. Install a fresh battery or set of batteries in your SWR meter if necessary.
- 2
  Turn the power switch of your SWR meter on and turn the selector switch to a setting such as "Antenna" or "A." Set the impedance or power selector dial or setting of the meter, if present, to the number of ohms that your antenna is rated for, which is almost always 50 for ham radio antennas.
- 3
  Connect the coaxial line to the "Antenna" jack of the SWR meter or touch the probe of the meter to the protruding exposed end of the line inside the coaxial cable fitting.
- 4
  Determine the SWR at the ham radio frequency of your choice by adjusting the tuning and frequency knobs or buttons on the SWR meter. Note the reading on the meter screen or dial. For instance, if you often broadcast or receive at 3.525 MHz, select that frequency with the appropriate controls of the meter. Repeat for as many frequencies as you wish.
- 5
  Find the lowest SWR at which your line operates by adjusting the frequency knob or button on the SWR meter until you get the lowest possible reading on the meter screen or dial. For example, you may see a reading of 1.2 at 14.325 MHz. Note this reading.
- 6
  Use the data to reposition, replace or otherwise change the setup of your antenna as necessary.

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